Report Summary

Country:
Spain

Development of improved binders for hot in-plant and cold in-situ recycling techniques

Hot recycling is actually carried out in asphalt mixing plants where a percentage of reclaimed asphalt is used. The amount of reclaimed asphalt employed depends mainly on plant limitations, on mixtures design and their final requirements as well. The fresh binder used will clearly contribute to the final mixture performance. Therefore, the development of binders for hot recycling performed within PARAMIX Project has focused on obtaining and improving the structural strength as well as the fatigue behaviour of the final mixtures (two different mixtures have been assessed) so that the life period of pavements can be increased. In that sense, the effect of polymer modification or the use of renewing agents has been evaluated concluding that the renewing agents do not clearly contribute in a positive way to the final behaviour of the mixture. Nevertheless, the employ of polymer modified binders has allowed the recycling of a porous wearing course replacing it also as a SMA wearing course. Considering this type of mixture, the employ of polymer modified binders is a requirement to fulfil due to the mixture characteristics. Also as an innovation of this stage can be considered the development of a polymer modified bitumen that will allow obtaining a final High Modulus Recycled Mixture (HMM). This kind of mixture is used in order to improve the strength of the pavement layers. The objective within PARAMIX Project was focused on verifying the contribution of high modulus polymer modified binders to the improvement of structural strength and fatigue behaviour of the final recycled pavement.

Cold in-situ recycling technique gives the advantage of recycling 100% of the old pavement. Nevertheless, this technique shows some drawbacks as it is the additional humidity required (in addition to the water contained in the emulsion) in order to do the compaction and coating steps. Therefore, the final cold mixture needs a curing time before being covered. This period will allow the humidity to be eliminated and in general a period of two or three weeks is a common delay. A controlled traffic circulation during this time will help the compaction of the cold recycled mixture. On the other hand, the cohesion increase of a cold recycled mixture is usually a slow process and consequently, it is necessary an immediate curing time that can last between two and six hours.

The development of emulsion formulae carried out within this Project has allowed, acting on the binder and aqueous phases of the emulsions, to obtain coated surfaces of the milled material over 90% keeping them during mixture, handling and compaction processes. It has also been possible the diminishment of the additional water needed in the process, getting at the same time good cohesion behaviours. The later would contribute to a possible reduction of curing periods, which is one of the main inconveniences of this technique. The employ of polymer modified bitumens as binders of these emulsions is also a novelty within this area and it is also expected from them a great contribution to the final cohesion behaviour, strength and fatigue behaviours of the recycled mixture. The influence of polymer modification, renewing agents as well as of lower penetration grades has been evaluated. Although it is necessary to take into account that a cold recycled mixture is a mixture in evolution within time, it has been observed from Experimental Tracks that a slight better behaviour has been obtained with renewing agents.